Circuit arrangement for phase or frequency modulated oscillations



Oct. 1954 E. H. HUGENHOLTZ 2,691,139

CIRCUIT ARRANGEMENT FOR PHASE 0R FREQUENCY MODULATED OSCILLATIONS Original Filed Oct. 1, 1948 IN VEN TOR.

Ell/an! Herman Hlyenh hf AQENT Patentecl Oct. 5, 1954 UNITED STATES ATENT OFFICE CIRCUIT ARRANGEMENT FOR PHASE R FREQUENCY MODULATED OS-CILLATIIONS Original application October 1, 1948, Serial No.

1950, Serial No. 154,087

3 Claims.

This application is a division of my application Serial No. 52,342 filed October 1, 1948, now abandoned.

This invention relates to circuit arrangements for phase or frequency modulated oscillations.

A method is known to interlock two unmodulated oscillations of like frequencies generated by two oscillators, according to which the compared oscillations are combined in a phase comparison device e. g. a diode-peak detector circuit, the output of the phase comparison device being fed through D. C.-passing connection including a low-pass filter having a low cut-off frequency, to frequency-control means associated with one of the oscillators so as to interlock as regards frequency both oscillators.

The invention is based on the recognition that appropriate modifications of the concerned type of circuit arrangements lead to circuit arrangements, which may be used advantageously in phase or frequency modulation transmitters, e. g. telegraphy transmitters with frequency-shift keying.

The circuit arrangement for phase or frequency modulated oscillations according to the invention is characterized by a first high-frequency oscillator with associated frequency modulator, a lower frequency generator comprising means to phaseor frequency-modulate its output by a modulation voltage, a heterodyning stage with inputs connected to said first high frequency oscillator and a second high frequency oscillator so as to heterodyne the first high frequency downward to a frequency substantially equalling said lower frequency, a phase-comparison-device with inputs connected to the heterodyning stage output and to the modulated lower frequency generator output, the output of the phase-comparison-device being connected to the input of the frequency modulator through a D. C.-passing filter passing said modulation-voltage so as. to automatically interlock as regards frequency and modulation the high frequency voltage and the phaseor frequency-modulated lower frequency voltage.

In a circuit arrangement according to the invention the interlocking of the first high frequency oscillator with the lower frequency generator and the preferably crystal-controlled second high frequency oscillator causes the central frequency of the first high frequency oscillator to show a stability determined by the stabilities of the lower frequency generator and the second high-frequency oscillator, which stability consequently may be very high, even if the output- Divided and this application April -5,

2 power of the first high frequency oscillator is many times the output-power of either of the other voltage-sources.

The invention will now be explained more fully by reference to the accompanying drawing showing, by way of example, an embodiment thereof.

In the drawing, the desired frequency-modulated oscillations are generated by means of a first high frequency oscillator l, the frequency of which is controlled by a control voltage supplied to a reactance tube 2 constituting a frequencymodulator associated with this oscillator. The oscillations generated by the oscillator l are mixed in a heterodyning stage 3 with oscillations generated by a crystal controlled second high frequency oscillator 4. The generated mixed oscillation, the central frequency of which is much lower than the central frequency of the oscillations generated by the oscillator I, is supplied to a phase-comparison device 5 or so called beat discriminator with a mixing stage of conventional type, together with an oscillation of substantially like frequency generated by a lower frequency generator 6, of which the output is modulated by means of a frequency-modulator, controlled by source 8 of modulating audio voltages. The voltage generated across an output resistance [3 of the phase-comparison device, which voltage is dependent of the phase difference between the oscillations generated in the output of heterodyning stage 3 and the oscillations generated by the lower frequency generator 6, controls the frequency-modulator 2 of the first high frequency oscillator I, thus ensuring, that the frequency of the oscillation generated by the oscillator I equals the sum (at reversed polarity of the control-voltage the difierence) of the frequencies generated by the oscillators 4 and 6. By means of a D. C.-passing low-pass filter ll undesired mixing frequencies are suppressed, but the timeconstant of the filter must be sufliciently small so as to pass all modulation frequencies of source 8. The desired FM-modulated output may be derived from terminals Hi provided in the output circuit of the first high frequency oscillator l.

The stages shown in the drawing are intended only as an example and may be substituted by any other stage suitable for the same purpose.

I claim:

1. In wavelength modulation apparatus, first and second sources for respectively producing first and second high-frequency signals, a third source for producing low-frequency oscillations, means to wavelength modulate said third source with an intelligence signal, a frequency corrector coupled to said first source, a mixing stage coupled to said first and second sources for heterodyning said first and second high-frequency oscillations to produce output beat oscillations whose frequency substantially equals the frequency of said low-frequency oscillations, a phase comparison device coupled to the output of said mixing stage and said third source to compare said wavelength modulated low-frequency oscillations and said heterodyned oscillations to produce a control voltage dependent on the wavelength difference therebetween, and means including a low-pass filter for direct coupling of said device with said frequency corrector to supply said control voltage to said frequency corrector whereby said first high-frequency oscillations are automatically interlocked both as to frequency and as to modulation with said wavelength modulated low-frequency oscillations.

2. Apparatus as set forth in claim 1 wherein said second source is constituted by a crystalcontrolled oscillator.

3. In wavelength modulation apparatus, first and second sources for respectively producing first and second high-frequency signals, a third 5 sources for heterodyning said first and second high-frequency oscillations to produce output beat oscillations whose frequency substantially equals the frequency of said low-frequency oscillations, a phase comparison device coupled to the output of said mixing stage and said third source for comparing said wavelength modulated lowfrequency oscillations and said beat oscillations to produce a control voltage dependent on the wavelength difference therebetween, and means including a low-pass filter having a cut-off frequency which substantially equals the highest wavelength modulation frequency of said signal for direct coupling of said device with said frequency corrector to supply said control voltage to said frequency corrector, whereby said first high-frequency oscillations are automatically interlocked both as to frequency and as to modulation with said wavelength modulated low-frequency oscillations.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,394,393 Mayer Feb. 5, 1946 2,400,648 Korman May 21, 1946 2,595,608 Robinson et al May 6, 195 2,605,425 Hugenholtz July 29, 1952 

